Alloy



Patented Apr. 16, 1935 UNITED STATES PATENT FFlE ALLOY No Drawing.

Application October 4, 1933, Se-

rial No. 692,138. Renewed October 16, 1934 2 Claims.

The invention relates to magnesium-base alloys and is directed to thedevelopment of alloys of this class which have good corrosionresistance, particularly in the cast and in the cast and heat treatedcondition.

The art of casting magnesium presents many practical difliculties whichmust be surmounted before the true commercial possibilities of magnesiumcastings can be fully realized. An alloy which is suitable for oneapplication may be entirely unsuited to another and, as a consequence,it is frequently necessary to sacrifice desirable characteristics of thealloy in order to more fully realize the advantages of some one or moreimportant characteristics. Thus a compromise must quite frequently bemade in order to approach in one alloy the optimum properties for agiven application. For example, it may be found that corrosionresistance can be sacrificed to a certain extent to obtain highertensile strength, yield point, hardness, or similar mechanicalproperties. Again, tensile strength may be sacrificed in order to obtainproper casting or working characteristics. It is an object of thepresent invention to develop magnesium alloys which will combine to amaximum degree the characteristics of corrosion resistance, favorablemechanical properties, workability, susceptibility to improvement byheat treatment and adaptability to sand casting.

A further object is the provision of magnesium alloys characterized bytheir susceptibility to be improved in mechanical properties by suitablethermal treatments. A further object is the provision of magnesium-basealloys characterized by good corrosion resistance in either the cast orin the cast and heat treated condition. A further object is theprovision of magnesium alloys possessing excellent castingcharacteristics. A further object is the provision of magnesium-basealloys susceptible, within certain ranges, to mechanical deformation.

I have discovered that magnesium-base alloys containing from 0.5, percent to 22 per cent of lead possess to an appreciable degree thecollective characteristics of alloys which are resistant to corrosion,alloys which may be readily cast,

- alloys which are susceptible to alteration of properties by thermaltreatments, alloys having favorable mechanical properties, and alloyswhich, within a restricted range, may be worked by extrusion, forging,or other means of mechanical deformation.

In accordance with my invention lead may be present in amounts as low as0.5 per cent, The

preferred casting alloys are those containing above about 5 per cent oflead since it is in these alloys that the most pronounced combination ofthese dilferent properties is obtained. The alloy may be worked byextrusion over a range of from about 0.5 per cent to about 22.0 per centof lead. As an all around casting alloy I have found a magnesium alloycontaining 5 to per cent of lead to be particularly adapted to generalfoundry purposes. Alloys falling within this preferred range ofcomposition as well as other alloys comprised within the broader limitspreviously defined, have been subjected to severe tests designed toproduce accelerated corrosion. Sand cast test bars poured in accordancewith the best casting practice in the art were subjected to corrosiontests in the as cast and in the heat treated condition. In the examplereferred to the heat treatment was carried out at about 459 centigradefor about 20 hours followed by quenching in water, and both heat treatedand unheat treated test bars were subjected to that corrosion test whichcomprises alternately immersing the metal calcium, cadmium and zinc.These may be added singly or in combination with each other, the zinc inamounts between about 1.0 per cent and 10.0 per cent, the calciumbetween about 0.1 per cent and 2.0 per cent, and the cadmium betweenabout 1.0 per cent and 10.0 per cent. These alloying elements aresubstantial equivalents as indicated by their susceptibility to thermaltreatment in magnesium-lead alloys. The calcium favorably afiects thecasting properties of the alloy without markedly decreasing itscorrosion resistance. For instance, a magnesium alloy containing 21.4per cent of lead and 0.25 per cent of calcium shows, in the as castcondition, a strength loss of only 17 per cent after alternate immersionin a 3 per cent sodium chloride solution for about 80 hours, while aheat treated magnesium alloy containing about 5 per cent of lead towhich about 0.25 per cent of calcium had been added did not undergo anyappreciable loss in strength under the foregoing corrosion conditions;the heat treatment in this case was a treatment at about 450 centigradefor about 20 hours. An alloy at magnesium with about 5.1 per cent 01lead and 10.0 per cent of cadmium had in the sand cast condition atensilestrength of about 24,650 pounds per square inch and an elongationof about 9.8 per cent in 2 inches. After a heat treatment of about 20hours at about 450 centigrade its tensile strength had increased toabout 25,140 pounds per square inch and its elongation to 10.3 per centin 2 inches. After an alternate immersion corrosion test for 80 hoursthe loss in strength was only 30 per cent. A similar result was obtainedwith a magnesium-base alloy containing about 5.3 per cent of lead andabout 5.0 per cent of cadmium. An alloy of magnesium with about 5.0 percent of lead and 5.0 per cent of zinc had in the sand cast condition atensile strength of about 23,370 pounds per square inch. After a thermaltreatment of about 20 hours at 450 centigrade followed by an agingtreatment of about 20 hours at 150 centigrade its strength had increasedto about 25,710 pounds per square inch. After an alternate immersioncorrosion test of 80 hours the loss in strength was only 12 per cent.Another alloy of magnesium with about 5.2 per cent of lead and 3.2 percent of zinc under similar conditions lost only about 10 per cent after80 hours alternate immersion in the corrosive solution. As a preferredcomposition for alloys of this nature I advise (l) 5.0 per cent lead,1.0 per cent calcium, balance magnesium; (2) 5.0 per cent lead, 5.0 percent cadmium, balance magnesium; (3) 5.0 per cent lead, 5.0 per centzinc, balance magnesium. If more than one of the elements calcium,cadmium, or zinc be present simultaneously, I prefer not to exceed atotal of 10.0 per cent for these elements.

One of the disadvantages of the alloys described herein which may affecttheir use in certain applications, particularly where high strength is aleading or very material consideration, is the fact that the grainstructure of these alloys (with or without calcium) tends to be coarse.I have found that the metals'aluminum and silicon form a class ofalloying elements which may be added to magnesium-lead alloys and aresubstantially equivalent in this respect that they materially refine thegrain structure of the alloy. Aluminum, for instance, can be added overa wide range, such as between 1.0 and 15.0 per cent; silicon may beeffectively present for this purpose in amounts of about 0.1 to 2.0 percent. When used in combination it is advisable that the total content ofaluminum and silicon does not exceed 15.0 per cent. In the preferredpractice of my invention I have found that the best results are usuallyobtained when the aluminum is present in amounts between 5 and 10 percent.

As a preferred magnesium-lead-silicon composition I use a magnesium-basealloy containing 7.0 per cent of lead and 0.5 per cent of silicon. As apreferred magnesium-lead-aluminum alloy I use a magnesium-base alloycontaining 7.0 per cent of lead and 5.0 per cent of aluminum. When thealuminum and silicon are used in conjunction I prefer to use a total ofabout 5.0 per cent of aluminum and silicon combined, for instance about4.0 per cent aluminum and 1.0 per cent silicon.

Manganese alone may be added to magnesiumlead alloys in amounts between0.1 per cent and 1.0 per cent and has a stabilizing effect upon thealloy properties in that it raises the hardness slightly, does. notmaterially decrease the corrosion resistance, and adds to the matrix ofthe alloy a hardening element which expresses itself not only in anincrease in tensile strength but also in surface hardness. An alloy ofthis nature containing about 8.0 per cent of lead and 0.85 per cent ofmanganese lost only 6 per cent of its original strength after 80 hoursalternate immersion in a 3 per cent aqueous solution of sodium chlorideand in the solutionheat treated condition lost only '7 per cent of itsstrength in the alternate immersion treatment. A magnesium alloycontaining about 10.37 percent of lead had lost only about 10 per centof its strength at the expiration of this period as compared withcertain other commercial alloys, such as, for instance, the well knownmagnesium alloy containing about '7 per cent of aluminum and 0.4 percent of manganese which, at the end of hours of alternate immersion, hadlost about 60 per cent of its strength.

Very favorable alloys can be compounded by using as a base an alloy ofmagnesium, lead and aluminum and making additions thereto of at leastone of the class of metals tin, manganese or zinc. The lead can be usedin amounts from about 0.5 per cent to about 22.0 per cent, the aluminumfrom about 1.0 per cent to about 15.0 percent, the tin from about 1.0per cent to about 15.0 percent, the manganese from about 0.1 per cent toabout 1.0 per cent, and the zinc from about 1.0 per cent to about 10.0per cent. A sand cast alloy within this range had, in the as castcondition, a tensile strength of 27,500 pounds per square inch and anelongation of 5.7 per cent in 2 inches. After a thermal treatment of 16hours at 315 centigrade, the alloy had a tensile strength of 29,640pounds per square inch and an elongation of 6.0 per cent in 2 inches.Some of the heat treated specimens were then given an alternateimmersion treatment for 40 hours and after the treatment the specimenshad a tensile strength of 28,413 pounds per square inch and anelongation of 5.8 per cent in 2 inches, this alloy containing 5.0 percent of aluminum, 5.0 per cent of lead, 0.4 per cent of manganese and2.0 per cent of zinc. The loss in strength on the corrosion treatment isobserved to be less than 5 per cent as compared to about 60 per centwith the commercial magnesiumealuminum-manganese alloy disclosedhereinbefore which contains about 7 per cent of aluminum and 0.4 percent of manganese. As preferred compositions for alloys of this nature Iadvise (1) 7.0 per cent of lead, 7.0 per cent of aluminum, 2.0 per centtin, balance magnesium; (2) 7.0 per cent lead, 7.0 per cent aluminum,2.0 per cent tin, 0.5 per cent manganese, balance magnesium; (3) 7.0 percent lead, 7.0 per cent aluminum, 2.0 per cent tin, 2.0 per cent zinc,balance magnesium.

Two alloy compositions within this range which I have used to advantageare as follows: A magnesium-base alloy containing 8.0 per cent ofaluminum, 3.0 per cent of lead, 0.4 percent of manganese, 1.0 per centof zinc, and 3.0 per cent of tin; a magnesium-base alloy containing 8.0per cent of aluminum, 1.0 per cent of lead, 0.4 per cent of manganese,1.0 per cent of zinc, and 1.0 per cent of tin.

The addition of lead to the magnesium-aluminum-manganese alloysincreases very considerably the corrosion resistance of these alloys,since with the addition of about 7 per cent of lead to an alloycontaining 7 per cent of aluminum and 1 per cent of manganese, the lossof strength after the alternate immersion test was only about 30 percent, as compared with about 60 per cent of the same alloy without lead.

Alloys of magnesium with lead, aluminum, and

manganese have been disclosed hereinabove. I

have discovered that if to a base alloy ofmagnesium-lead-aluminum-manganese I add one or more of the class ofmetals calcium or cadmium, the resulting alloys become considerably moresusceptible to varation of properties by thermal treatments and theirhardness can be markedly increased by artificial aging after thermalsolu tion treatments. In these alloys the lead content should range fromabout 0.5 per cent to about 22.0 per cent, the aluminum from about 1.0per cent to about 15.0 per cent, and the manganese from about 0.1 percent to about 1.0 per cent. To these elements as a common base I add theelements calcium, or cadmium, singly or in combination, the calcium inamounts from about 0.1 per cent to about 2.0 per cent, the cadmium fromabout 1.0 per cent to about 10.0 per cent. As an example of an alloy ofthis nature, a sand cast specimen of a magnesium-base alloy containingabout 10.0 per cent of lead, about 7.0 per cent of aluminum, about 0.4per cent of manganese, and about 5.0 per cent of cadmium, had in thecast condition a tensile strength of about 23,200 pounds per squareinch. After a thermal solution treatment of 21 hours at about 430centigrade the tensile strength of the alloy had increased to about36,000 pounds per square inch, 2. gain in strength of about 55 per cent.The same alloy after the solution treatment had a Brinell hardness ofabout 61 and this hardness was raised to about 84 by an additional agingtreatment of 20 hours at about 175 centigrade, the tensile strengthincreasing slightly to about 37,000 pounds per square inch.

Similarly a magnesium-base alloy containing about 5.0 per cent of lead,7.0 per cent of aluminum, 10.0 per cent of cadmium, and 0.4 per cent ofmanganese had in the sand cast condition a tensile strength of about24,000 pounds per square inch. After a thermal treatment of 21 hours atabout 430 centrigrade the alloy had a tensile strength of about 35,000pounds per square inch. An additional aging treatment raised the Brinellhardness of the alloy from about 61 to about 79.

Similarly, a magnesium-base alloy containing about 5.0 per cent of lead,10.0 per cent of cadmium, 7.0 per cent of aluminum, 1.0 per cent ofmanganese, and 0.25 per cent of calcium had in the sand cast condition atensile strength of about 24,290 pounds per square inch. After a thermaltreatment of 20 hours at about 430 oentrigrade this alloy had a tensilestrength of about 33,200 pounds per square inch. After an additionalthermal treatment of about 20 hours at about 150 centigrade the strengthincreased to about 35,600 pounds per square inch and the Brinellhardness from about 47 to about 66.

Another magnesium-base alloy containing about 10.0 per cent of lead, 7.0per cent of aluminum, 5.0 per cent of cadmium, 0.4 per cent of maganese,and 0.1 per cent of calcium, had in the sand cast condition a tensilestrength of about 23,210 pounds per square inch. After a thermalsolution treatment of 21 hours at about 430 centigrade the alloy had atensile strength of about 36,030 pounds per square inch; the Brinellhardness was about 61. After an additional aging treatment of about 20hours at about 175 centigrade its tensile strength was about 37,010pounds per square inch and its Brinell hardness about 84. As a desirablealloy of this nature I advise 7.0 per cent lead, 7.0 per cent aluminumand 0.4 per cent manganese. If more than one of the elements calcium orcadmium are present simultaneously, the total should not exceed about10.0 per cent for preferred purposes.

The addition of zinc in amounts from about 1.0 per cent to about 10.0per cent to magnesiumlead alloys containing aluminum and silicon incombination decreases the linear shrinkage, thus favorably afiecting thecasting properties, and. also increases the corrosion resistance andraises the yield point of these alloys. In alloys of this type the leadshould range from 0.5 per cent to 22.0 per cent, the aluminum from 1.0per cent to 15.0 per cent, and the silicon from 0.1 per cent to 2.0 percent, but the total amount of aluminum and silicon should preferably notexceed 15.0 per cent.

A useful alloy of this nature is a magnesiumbase alloy containing about10.0 per cent lead, 8.0 per cent aluminum and 3.25 per cent zinc.Another useful composition is attained by substituting about 1.0 percent silicon for part or all of the aluminum.

An alloy similarly improved in casting properties, although not to sucha decided extent, is one containing from about 0.5 per cent to 22.0 percent of lead, from about 1.0 per cent to about 10.0 per cent of zinc,and from about 0.1 per cent to about 2.0 per cent of silicon. Afavorable alloy within this range is a magnesiumbase alloy consisting ofabout 10.0 per cent of lead, about 3.25 per cent of zinc, and about 1.0per cent of silicon, the balance being substantially magnesium.

In making up alloys of the compositions disclosed hereinabove the alloysmay be compounded by any of the methods known in the art. In casting thealloys recourse may be had to the protective measures disclosed inexisting patents and the published literature relating to easilyoxidizable metals. The alloys. especially the magnesium-lead binaryalloys, may be extruded; over the entire disclosed composition range,but other types of mechanical deformation such as rolling or forgingshould be carried on with due regard for the fact that as the percentageof total added alloying elements increases, the necessity for precautionin working the alloy also increases.

It is my object to retain, as far as possible, the advantages of the useof magnesium base, such as low specific gravity, while securing inaddition the hereinabove disclosed benefits accruing from the additionsof the other alloying elements herein outlined. Accordingly, where inthe appended claims the term magnesium-base alloy is used, it refers toan alloy containing more than approximately 50 per cent of magnesi Thisapplication is a continuation in part of my copending application SerialNo. 643,052,"filed November 17, 1932.

What I claim is:

l. A magnesium-base alloy containing from 0.5 to 22.0 per cent of lead,from 1.0 to 10.0 per cent of zinc, 1.0 to 15.0 per cent of aluminum. and0.1 to 2.0 per cent of silicon, the balance being substantially allmagnesium.

2. A magnesium-base alloy containing about 10.0 per cent of lead, about7.0 per cent of ,aluminum, about 1.0 per cent of silicon and about 3.25per cent of zinc, the balance being substantially all magnesium.

ROY E. PAINE.

